The invention relates to apparatus and methods for producing a cutting edge on a razor blade strip of preferred geometry and more particularly the formation of a substantially convex final facet.
Razor blades are generally produced by a series of grinding and honing operations intended to achieve a degree of sharpness and durability consonant with modern standards. U.S. Pat. No. 2,709,874 issued to Delafontaine discloses and illustrates razor blade grinding and honing equipment of the type utilized in the fabrication of razor blades. The equipment disclosed therein may be utilized with modification in the practice of the present invention.
In attempting to minimize possible defects in the formation of the ultimate edge of the razor blade and to achieve greater durability and shaving comfort the prior art has employed various modifications in grinding and honing techniques U.S. Pat. No. 3,461,616 to Nissen et al discloses a method and apparatus intended to produce an improved razor blade conformation. This patent employs a final honing stage in which the honing wheels are dressed to have a substantially hyperbolic frustoconical geometry. The imposition of these wheels against the moving blade strip at an inclined angle of approximately 5 degrees produces a razor blade having a convex final facet, i.e., the included angle of the ultimate edge is some selected maximum value which diminishes in proportion to its distance from such ultimate edge. This geometry presents a continuous relief to the hair as it is being cut. It also provides a stronger blade edge in that the cross-sectional convexity permits increased included angle and commensurate blade thickness nearer the ultimate edge of the blade. This process also minimizes defects known as "spot turn". This defect, which shows itself in a lateral periodic displacement of the ultimate edge from the axial plane of the blade strip, is essentially caused by the unequalized lateral forces exerted on the edge by the trailing or exit edges of the final honing wheels which are helically shaped so as to permit their intermeshing.
The method and apparatus of U.S. Pat. No. 3,461,616 demands use of honing wheels having precise conformance to a particular geometry and which must be precisely aligned at an inclined angle to the path of the blade edge during the grinding process. These requisites add to the expense and complexity of an already difficult process and to this degree are undesirable. Thus, it is an object of the present invention to overcome the disadvantages and complexities of the prior art, and to provide an improved method and apparatus for forming a sharpened blade edge.
Another object of the invention is to provide an improved method and apparatus for producing a stronger razor blade edge.
Another object of the invention is to provide a method and apparatus which minimizes damage to the ultimate edge of the razor blade during the production thereof.
Still another object of the invention is to provide for final honing of the ultimate edge of a razor blade exhibiting increased durability and shaving comfort.
In furtherance of the foregoing objects the present invention contemplates formation of a final facet on the ultimate edge of a razor blade having substantially convex geometry and freedom from defects. Razor blade strip is drawn along a defined path at a controlled linear velocity. Grinding means disposed in this path form a facet on the edge of the strip, and first honing means located on this same path but remote of the grinding means forms a first facet on the strip. The final facet is produced by final honing wheels mounted adjacent to the path of the strip on opposing sides thereof. The wheels have helical circumferential grooves cut therein which when intermeshed form a nip of predetermined axially length parallel to the strip and contiguous therewith. This nip defines a predetermined included angle between the final facets located on opposing sides of the blade strip. The final honing wheels are selected to have sufficient resiliency to produce the desired final facet of substantially convex geometry and minimum edge defects.